Twin Engines, Twin Fuel Tanks, Different Fuel Consumption?

[Sundancer]

The previous owner of our boat stated that whenever he filled up his twin 70 gallon tanks, one tank always used 3 - 5 gallons more than the other tank. I attributed this to the engine tune, prop tune, carburetor differences or some combination of all of the above. Have others experienced this and is it common for the Port to always burn more than Starboard or is it just random? Just wondering. He had some theory of hydrodynamics going since the props rotated the same direction. I didn't quite get it or buy it but figured I'd post it here to see what your experience has been.

 

[Four Suns]

My experience on my boat has been that historically the port engine burns a little more fuel (0.5 gph when each is burning around 22 gph) than the starboard engine. My props rotate in different directions and the port transmission has different gearing than the starboard to make this work.

I did find this out though a few weeks ago. If I open the hatch in the cockpit, the load factor, fuel burn, boost pressures, etc. are about identical whereas with the hatch closed, the port engine seems to have to work a tad harder. My port engine air intake is in the middle of the engine room whereas the starboard is against the hull vent so I would think the port engine is drawing in warmer air than the starboard.

I posted a thread on this here:

http://clubsearay.com/forum/showthread.php?t=4846&page=3

I don't worry about it now...

 

[Pirate]

Generator.

 

[LMBoat]

I have twin 7.4's <carbs>. If my fuel computer and calculations are correct, my port engine does burn 5-10% more fuel then the strb. The genset pulls off the strb tank and the strb tank is smaller <108 gal, vs 117 on the port side>. It is almost as it Searay expected the port to burn more. The compression in both engines is great and everything else with engines seem fine. All the items mentioned seem logical and I have not really worried about it. I have 1,500 hours on mine and all is well <today>

 

[Sundancer]

Generator.

The Generator!! I don't have one, nice try though!!

I guess there is something to it, but who knows what! At least I'm consistent with what others have experienced. I didn't think about the intake air and I wonder if it has something to do with the P-factor(Something we talk about with prop torque in airplanes)? I'll see the previous owner and forward that to him.

 

[skolbe]

My Port Engine burns about a half gallon more per hour according to Smartcraft. Fairly common a friends Larson 330 does the same thing.

 

[comsnark]

I would not undersestimate the impact of the "AIR" distribution.

Warmer vs colder air, or restricted air flow to the engine can make a HUGE difference in performance.

You engines will only get identical peformance if the air conditions are identical.